Handling rolls of material, particularly large, heavy rolls of material, involves unique and substantial obstacles that must be overcome. Such large rolls of material are typically created by wrapping the particular material around a hollow core, which is rotated on a mandrel or pair of spindles.
With respect to certain types of materials, such as paper and other delicate materials, the rolls must be carefully handled to avoid damage to the material. Such rolls of material have traditionally been transported in a variety of ways to prevent direct contact with, and therefore damage to, the material. One of the most common transportation and handling methods involves inserting a rod connected to a lift device into the hollow core of the roll, and then lifting the roll with the rod. This method prevents contact with the material on the outside of the roll.
Another known method of lifting rolls without contacting the surface of the material involves creating a vacuum on one end of the roll. The vacuum force is then used to lift and transport the roll. This method of transportation and lifting allows the rolls to be stored vertically, by placing the rolls on their ends. Storing the rolls on their ends allows storage space to be used more efficiently (rolls can even be stacked on top of one another), and reduces the contact area between the lifting device and the roll.
Using a vacuum force to lift rolls of material creates a unique set of handling problems, particularly in the case of large paper rolls for newsprint. An effective and economical seal must be created at one end of the roll so that a vacuum can be produced on the opposite end for transporting the roll by means of a vacuum lift device. The device used for sealing one end of the roll should be effective, yet relatively easy to install and remove when necessary.
One known type of sealing device is a plug formed from compressed wood and glue. The outer surface of the wood plug slopes continually from a narrowed end (inserted first into the core) to a wide end. The wood plug is inserted into an end of the core to plug up the opening. The plug must overcome an interference fit with the core after it has been completely inserted to form a proper seal.
Use of wood as a core plug material has several drawbacks. Recently, the cost of wood has increased dramatically. Also, a core made of compressed wood and glue is heavy, which creates substantial additional costs in transporting the plugs. The compressed wood plugs also break down structurally when exposed to moisture.
Known compressed wood plugs either have a central aperture or are solid. A solid compressed wood core plug is difficult to remove from the core once installed. If the compressed wood plug has a central aperture for handling and installation purposes, the aperture must be plugged in order to create a vacuum on the opposite end of the roll. Attempts to suitably seal such apertures in compressed wood plugs in order to create a vacuum have heretofore been unsuccessful.
Accordingly, there is a need to develop a core plug that is insertable into the ends of a core around which material is wrapped, that will seal one end of the core to enable a vacuum lift force to be created on the opposite end for transportation purposes, that will enable the roll to be installed onto spindles of a reel without having to remove the core plugs, and that will provide sufficient axial and radial strength to support the roll through the core plugs once installed upon a pair of spindles. The present invention involves a core plug which provides substantial and surprising benefits in this regard. The various objects, features, and advantages of the invention will become apparent from the detailed disclosure that follows.